Microelectromechanical device packages with integral heaters

ABSTRACT

A microelectromechanical device package with integral a heater and a method for packaging the microelectromechanical device are disclosed in this invention. The microelectromechanical device package comprises a first package substrate and second substrate, between which a microelectromechanical device, such as a micromirror array device is located. In order to bonding the first and second package substrates so as to package the microelectromechanical device inside, a sealing medium layer is deposited, and heated by the heater so as to bond the first and second package substrates together.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention is generally related to the art ofmicroelectromechanical device packages, and more particularly, tospatial light modulators having micromirror device packages withintegral heaters.

BACKGROUND OF THE INVENTION

[0002] Micromirrors are key components of microelectromechanical system(MEMS)-based spatial light modulators (SLM). A typical MEMS-based SLMusually consists of an array of miniature micromirrors. Thesemicromirrors are selectively deflected, for example, in response to anelectrostatic force, which in turn selectively reflect incident light toproduce digital images. Such micromirrors, however, are extremelysensitive to contamination, such as moisture and dust. Thiscontamination has varying effects on the micromirrors, fromcapillary-condensation and post-release stiction to deterioration of themicromirror surfaces. Such effects can cause mechanical failure of themicromirrors in operation. For this and other reasons, micromirror arraydevices are often packaged after releasing.

[0003] Regardless of differences of the packaging methods currentlydeveloped for a micromirror array device, two substrates, one forsupporting the device and another one for covering the device, andsealing medium(s) for bonding the two substrates are utilized. Most ofthe sealing mediums require application of heat during bonding. However,the heat, if not properly applied, may degrade the micromirror arraydevice. For example, improperly applied heat may change the desiredmechanical properties of the micromirrors. It may also thermallyactivate particles, such as impurities and particles making up themicromirrors, prompting diffusion of these activated particles withinthe micromirrors, thus exacerbating degradation of the micromirrors. Orheat may decrease anti-stiction materials within the package.

[0004] Therefore, a method and an apparatus are needed for packagingmicromirror array devices.

SUMMARY OF THE INVENTION

[0005] In view of the forgoing, the present invention provides anapparatus for packaging micromirror array devices and a method ofpackaging micromirror devices using the same. In order to package themicromirror device, a first and second substrate is provided. Themicromirror array device is accommodated within a cavity formed by thefirst and second substrate. During packaging, one or more sealingmediums that are applied between the first and second substrate aresoldered by at least a heater that is formed along the periphery of thesurface of either the first or the second substrate and embeddedunderneath said surface of said substrate. The first and the secondsubstrates are then bonded through the soldered sealing mediums.

[0006] According to an embodiment of the invention, a substrate of apackage for packaging a micromirror array device is provided therein.The substrate comprises: a laminate that comprises a plurality ofsubstrate layers bonded together; and a heater that is disposed along aperiphery of one substrate layer of the plurality of substrate layersand disposed between said substrate layer and another substrate layer ofthe plurality of substrate layers.

[0007] According to another embodiment of the invention, a package isprovided. The package comprises: a first substrate having a heater alonga periphery of a surface of the first substrate and underneath saidsurface; a second substrate above the first substrate; a semiconductordevice or a microelectromechanical system device between the first andsecond substrate; and a first sealing medium layer between the firstsubstrate and the second substrate.

[0008] According to a further embodiment of the invention, a method ofpackaging a micromirror array device is disclosed. The method comprises:providing a first package substrate that comprises a heater integralwith and along a periphery of one surface of the first substrate;attaching a semiconductor device or a microelectromechanical device tothe first substrate; depositing a first sealing medium layer on thesurface of the first substrate; placing a second substrate on the firstsealing medium layer; driving an electric current through the heater soas to generate heat for melting the first sealing medium; and bondingthe first and second substrate by the melted sealing medium layer.

[0009] According to another embodiment of the invention, a system isprovided. The system comprises: a light source for providing an incidentlight; a spatial light modulator for selectively modulating the incidentlight so as to form an image on a display target, wherein the spatiallight modulator further comprises: a first package substrate having aheater along a periphery of one surface of the first package substrateand embedded underneath said surface for generating heat; a micromirrorarray device held on the first package substrate; a second packagesubstrate on the first package substrate; a first sealing medium layerdeposited between the first and second package substrate; and whereinthe first and second package substrate is bonded together through thefirst sealing medium layer; a condensing optical element for directingthe incident light onto the spatial light modulator; a display target;and a projection optic element for directing the modulated light ontothe display target.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] While the appended claims set forth the features of the presentinvention with particularity, the invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings ofwhich:

[0011]FIG. 1a is a diagram schematically illustrating a packagingsubstrate for packaging a micromirror array device, the packagingsubstrate having a heater that is formed along the periphery of onesurface of the substrate and embedded underneath said surface of saidsubstrate according to an embodiment of the invention;

[0012]FIG. 1b is a cross-sectional view of the package substrate of FIG.1;

[0013]FIG. 2a is a diagram schematically illustrating a packagingsubstrate for packaging a micromirror array device, the packagingsubstrate having a heater formed along the periphery of one surface ofthe packaging substrate, and wherein the heater has a zigzag edgeaccording to another embodiment of the invention;

[0014]FIG. 2b is a cross-sectional view of the packaging substrate ofFIG. 2a;

[0015]FIG. 3 is a diagram schematically illustrating a packagingsubstrate having a heater that is laminated between two layers of saidpackaging substrate according to another embodiment of the invention;

[0016]FIG. 4a is a diagram schematically illustrating a micromirrorarray device that is packaged using a packaging substrate in FIG. 1according to another embodiment of the invention;

[0017]FIG. 4b is a cross-sectional view of the package in FIG. 4a;

[0018]FIG. 5a is a diagram schematically illustrating a micromirrorarray device that is packaged using a packaging substrate in FIG. 1according to yet another embodiment of the invention;

[0019]FIG. 5b is a cross-sectional view of the micromirror array packageof FIG. 5a;

[0020]FIG. 6a is a diagram schematically illustrating a micromirrorarray device that is packaged using a packaging substrate of FIG. 3according to yet another embodiment of the invention;

[0021]FIG. 6b is a cross-sectional view of the micromirror array deviceof FIG. 6a;

[0022]FIG. 7 is a diagram schematically illustrating a packagedmicromirror array device;

[0023]FIG. 8a is a simplified display system employing the packagedmicromirror array device of FIG. 7;

[0024]FIG. 8b is a block diagram illustrating an exemplary operation ofa display system employing three packaged micromirror array devices ofFIG. 7;

[0025]FIG. 8c is a diagram schematically illustrating a display systememploying three packaged micromirror array devices of FIG. 7;

[0026]FIG. 9a is a diagram schematically illustrating an exemplarymicromirror of the micromirror array;

[0027]FIG. 9b is a diagram schematically illustrating an exemplarymicromirror array consisting of the micromirror of FIG. 9a;

[0028]FIG. 10a is a diagram schematically illustrating another exemplarymicromirror of the micromirror array; and

[0029]FIG. 9b is a diagram schematically illustrating an exemplarymicromirror array consisting of the micromirror of FIG. 10a.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Turning to the drawings, the present invention is illustrated asbeing implemented in a suitable packaging process for micromirror arraydevices. The following description is based on selected embodiments ofthe invention and should not be interpreted as a limitation of theinvention with regard to alternative embodiments that are not explicitlydescribed herein.

[0031] Referring to FIG. 1a, a packaging substrate with an integralheater for packaging micromirror array devices is illustrated therein.As seen, packaging substrate 200 comprises substrate layer 210 andsubstrate layer 215. Substrate layer 210 has a concave surface thatforms a cavity in which micromirror array device can be placed. Onsubstrate layer 210, heater 220 is formed along the periphery of theconcave surface of substrate layer 210. Electric current from externalelectric power source can be introduced into heater 220 via two leads222 so as to generating heat. Heater 220 is laminated between substratelayers 210 and 215. A cross-sectional view of packaging substrate 200 isillustrated in FIG. 1b.

[0032] In a preferred embodiment of the invention, heater 220 has azigzag edge as shown in FIG. 1a. Alternatively, the heater can take anyother suitable forms, such as a set of consecutively connected straightlines (or disconnected lines each having leads at each end), coils orcombinations of lines and coils or zigzag lines. Other than forming theheater on substrate layer 210 which comprises a cavity for accommodatingmicromirror array devices, the heater can also be formed on substrate215. In particular, the heater can be formed on substrate 215 and on thesurface that faces substrate 210. As will be seen in FIG. 2a, substrate215 is not necessary, and if not provided, preferably heater 220 ispatterned on or otherwise integral with substrate 210. The heater can bemade of any suitable materials, such as tungsten, and can be formed byany suitable methods (e.g. sputtering and electro-plating) for making athin film and standard methods (e.g. printing) for making a thick film.In order to generating heat, electric current is driven through the twoleads 222. Alternatively, the electric current can also be introducedinto the heater through leads 223, which are formed on substrate layer215 and connected to the two leads 222 respectively.

[0033] Substrate layers 210 and 215 can be any suitable preferablynon-electrically conducting materials, preferably ceramic or glass, andmore preferably ceramic. Other materials (e.g. organic or hybridorganic-inorganic materials) could also be used depending upon theirmelting points. In another embodiment of the invention, substrate layers210 and 215 each can be a multilayered structure that further comprisesa plurality of substrate layers. In this situation, the top layer, onwhich the heater is disposed, of substrate 210 and the bottom layer,which face the heater, of substrate 215 are preferably non-electricallyconducting. Other layers, including the substrate layers underneath thetop layer of substrate 210 and the substrate layers above the bottomlayer of substrate 215 can be any desired materials, such as ceramic,glass and metallic materials.

[0034] Other than embedding the heater underneath the surface of thepackaging substrate, the heater can be formed on the surface of thepackaging substrate as shown in FIGS. 2a and 2 b. Referring to FIG. 2a,the heater is formed along the surface of substrate 210, and no othersubstrate layer is formed thereon. Substrate 210 could be a multilayeredstructure. The heater is directly exposed to other materials, such assealing mediums, and structures, such as other packaging substrates. Inthis situation, the sealing medium deposited on the heater is preferablynon-electrically conducting materials, such as glass frit.

[0035] As discussed above, substrate layer 210 has a concave surfacethat forms a cavity in which micromirror array device can be placed.Alternatively, the substrate layers can be flat plates, as shown in FIG.3. Referring to FIG. 3, substrate layers 266 and 262 of packagesubstrate 260 both are flat plates. Heater 220, which is formed onsubstrate layer 266 and along the periphery of the surface of substratelayer 266, is laminated between substrate layers 266 and 262. Similar tothe heater in FIG. 2a, an electric current can be driven through theheater via the two heater leads 222 for generating heat.

[0036] Other than forming heater 220 on substrate layer 266, the heatercan also be formed on substrate 262. In particular, the heater can beformed on substrate 262 and on the surface that faces substrate layer266. Similar to the substrate layers 210 and 215 in FIG. 2a, substratelayers 262 and 266 can be any suitable non-electrically conductingmaterials, preferably ceramic and glass, and more preferably ceramic. Inanother embodiment of the invention, substrate layers 266 and 262 eachcan be a multilayered structure that further comprises a plurality ofsubstrate layers. In this situation, the top layer, on which the heateris disposed, of substrate 266 and the bottom layer, which faces theheater, of substrate 262 are preferably non-electrically conductinglayers. Other layers, including the substrate layers underneath the toplayer of substrate 266 and the substrate layers above the bottom layerof substrate 262 can be any desired materials, such as ceramic, glassand metallic materials. Micromirror array device 105 can be attached tosubstrate layer 262 and supported thereby.

[0037] In the following, exemplary implementations of the embodiments ofthe present invention will be discussed with reference to packages ofmicromirror array devices and packaging processes for making the same.It will be understood by those skilled in the art that the followingexemplary implementations are for demonstration purposes only and shouldnot be interpreted by any ways as a limitation. In particular, althoughnot limited thereto, the present invention is particularly useful forpackaging semiconductor devices or micromirror array devices. Thepackages with integral heaters and methods of using the packages withintegral heaters can also be applied in packaging othermicroelectromechanical systems, such as MEMS-based optical switches,image sensors or detectors and semiconductor devices requiring lowtemperature hermetic sealing. Moreover, the following exemplaryimplementation will be discussed with reference to heaters with zigzagedges and packaging substrate with substantially rectangular shapes forclarity and demonstration purposes only. Other variations of the heatersand the packaging substrates without departure from the sprit of thepresent invention may also be applicable. For example, the heater may becomposed of a set of segments with each segment being a straight line, acoil, a zigzag line or other desired forms. For another example, thepackaging substrate layers can be any desired shapes, other than thepreferred rectangular shape.

[0038] Referring to FIG. 4a, a micromirror array device package usingthe packaging substrate with an integral heater in FIG. 1 is illustratedtherein. Specifically, micromirror array device 105 is paced in thecavity of packaging substrate 200, which comprises integral heater 220as shown in FIG. 1. A double substrate type micromirror device isillustrated, however, as in all the drawings, a single substrate device(e.g. micromirrors formed on silicon wafer) could be used. Coversubstrate 235, which is preferably glass, is provided for sealing themicromirror array device within the cavity. In order to bond coversubstrate 270 and packaging substrate 200, sealing medium 230,preferably one that forms a hermetic seal and has a melting temperatureof 300° C. or less, and preferably 200° C. or less, is disposed betweenthe cover substrate and packaging substrate as shown. Preferably thesealing material is an inorganic material such as a metal, metal alloyor metal compounds (e.g. a metal or metalloid oxide). Alternatively,sealing medium layer 230 can also be deposited directly on the surfaceof packaging substrate 200, or on the surface of the lower surface ofcover substrate 235, in which case, sealing medium layer 230 ispreferably deposited along the periphery of the lower surface of thecover substrate. Sealing medium 230 is preferably a material that isstable, reliable, cost-effective and has good thermal-properties (e.g.co-efficient of thermal expansion (CET), thermal-conductivity etc.)compatible with the other components, such as package substrate 200 andcover substrate 235, of the micromirror array device package. It isfurther preferred that sealing medium has a low melting temperature(when the sealing medium is non-metallic) or soldering temperature (whenthe sealing medium is metallic). Glass frit, such as Kyocera KC-700, isan acceptable candidate for the sealing medium. During the bondingprocess, an electric current is driven through the integral heater viathe two heater leads (i.e. leads 222) for generating heat. The amplitudeof the electric voltage is dominated by electric characteristics of theheater (e.g. electric properties of the material of the heater, theshape of the heater), thermal characteristics and geometry of thesubstrate layers of packaging substrate 200 and the desired temperatureon the surface of packaging substrate 200 for melting sealing medium(e.g. sealing medium layer 230). As an example, the melting temperature,also the desired temperature on the surface of packaging substrate 200,of sealing medium 230 is from 100 to 300° C., preferably around 350° C.The heater is embedded underneath the surface of the packaging substrateat a distance preferably from 1 millimeter to 10 millimeters, preferablyaround 7 millimeters. In this example, the packaging substrate isceramic. Then the voltage set up between the two heater leads 222 ispreferably from 40 to 100 volts, preferably around 70 volts. In otherwords, this voltage causes the heater generating heat with an amountthat raises the surface temperature of the packaging substrate to themelting temperature of sealing medium layer 230. As a result, sealingmedium is melted and used to bond cover substrate 235 and packagingsubstrate 200. Meanwhile, the temperature at the micromirror devicelocation is far less than the temperature that causes mechanical failureof the micromirrors of the micromirror device. In the embodiment of theinvention, the temperature at the micromirror device location ispreferably less than 70° C.

[0039] During the bonding process, external pressure may be applied tothe cover substrate, as shown in FIG. 4b, wherein a cross-sectional viewof FIG. 4a is illustrated therein. After a predetermined time periodwhen the cover substrate and the packaging substrate are securelybonded, the voltage, as well as the external pressure, can be withdrawn,but not necessarily at the same time. As shown in FIG. 4b, one or moregetters 325 can be provided within the package 270 for absorbingmoistures and impurity particles (e.g. organic particles) either sealedwithin the cavity or emitted from the components of package 270 duringthe packaging process, especially during the heating process.

[0040] Though cover substrate 235 it is preferably visible lighttransparent glass, it may also be other materials, such as metals ormaterials that are not transparent to visible light. In these cases,cover substrate 235 preferably comprises an inlay light transparentglass for allowing light to travel through and shine on micromirrorarray device 105. Alternatively, cover substrate 235 may have an openingforming window with a light transparent glass mounted on the window forallowing transmission of incident light. Moreover, a light blocking maskwith light blocking strips formed around the circumference of the maskmay be applied along cover substrate 235 for blocking incident light notshining on the surface of the micromirror array device. By this, opticalperformance, such as contrast ratio, of the micromirror array device canbe improved.

[0041] Other than using glass frit as sealing medium, other suitablematerials, such as solderable metallic materials, such as Au, BiSn_(x),AuSn_(x), InAg_(x), PbSn_(x), and copper, may also be used. However,most solderable metallic materials have poor adhesion to oxide materialsor layers that often form on surfaces of the substrates. To solve thisproblem, a metallization film is preferably employed to metalizing thesurface of the substrate before using solderable metallic sealingmediums, which will be discussed in further detail in the following.

[0042] Referring to FIG. 5a, sealing medium layer 245 comprises asolderable metallic material that is preferably stable, reliable,cost-effective and has thermal-properties (e.g. co-efficient of thermalexpansion (CET), thermal-conductivity etc.) compatible with the othercomponents, such as package substrate 200 and cover substrate 235, ofthe micromirror array device package, and more preferably has a lowsoldering temperature. In order to enhancing adhesion of sealing mediumlayer 245 to the surfaces of substrates 235 and 200, metallizationlayers 240 and 250 are provided for metalizing the lower surface ofcover substrate 235 and top surface of package substrate 200,respectively. Metallization mediums can be any suitable materials, suchas aluminum, gold, nickel or composition of two or more of suitablemetallic elements, such as gold/nickel, preferably a material with lowsoldering temperature. These materials can be deposited on the surfacesas thick or thin films using suitable deposition methods, such as thosestandard methods (e.g. sputtering) for depositing thin film and thosestandard methods (e.g. print and paste) for depositing thick films. Inan embodiment of the invention, metallization medium layer 250 is a thinlayer of noble metallic material, such as gold. This metallizationmedium layer is preferably deposited, such as sputtered as a film on thelower surface of cover substrate 235. Similarly, another metallizationlayer 240 is provided between sealing medium layer 245 and packagesubstrate 200 for metalizing the top surface of the package substrate.Metallization layer 240 is also preferably deposited, such as sputteredas a film on the upper surface of package substrate 200. Whenmetallization layers 250 and 240 are respectively deposited on the lowersurface of cover substrate 235 and the upper surface of substrate 200,these metallization layers may have high soldering temperatures. In thissituation, theses metallization layers are integral with cover substrate235 and substrate 200, respectively. Alternatively, metallization layers250 and 240, each could be a multilayered structure. As an example, themultilayered structure comprises a metal-oxide layer (e.g. CrO₂ andTiO₂), a metallic layer (e.g. Cr and Ti), a second metallic layer (e.g.Ni) and a third metallic layer (e.g. Au) on top. The metal-oxide layeris first deposited on the surface of the non-metallic substrate, such asceramic and glass, because it presents strong adhesion to thenon-metallic substrate's surface, which is generally oxidized. Themetallic layer generally comprises a metallic material that has strongadhesion to the metallic-oxidation layer. The second metallic layer isdeposited between the third metallic layer and the first metallic layerto prevent diffusion of the first metallic material into the thirdmetallic layer on top. As another example, metallization layer 240further comprises a tungsten layer, a nickel layer and a gold layer. Ofcourse, metallization medium layer 250 may also be a multilayeredstructure that further comprises a plurality of metallization layers asdesired. The third metallic layer on top, preferably comprises ametallic material having low oxidation. Exemplary metallic materials forthe third metallic layer are, Au, Cr and other noble metals.

[0043] During the packaging process, the integral heater embeddedunderneath the surface of package substrate 200 is electrically poweredfor generating heat so as to solder sealing medium layer 245 betweenmetallization layers 240 and 250. Meanwhile, external pressure may beapplied to the package for enforcing bonding package substrate 200 andcover substrate 235, as shown in FIG. 5b.

[0044] In another embodiment of the invention, cover substrate 235 mayalso have a heater. As the heater (e.g. heater 220) in package substrate200 as described with reference of FIG. 1a, the heater in coversubstrate 235 can be formed along the periphery of the surface of thecover substrate and embedded underneath said surface of the coversubstrate. This heater in the cover substrate can be used in bonding thecover substrate and the package substrate. And it is especially usefulin soldering metallization medium layer 250 and sealing medium layer245.

[0045] A cross-section view of package 275 in FIG. 5a is illustrated inFIG. 5b. As seen, other features, such as getters 325 can be providedfor absorbing moisture.

[0046] Referring to FIG. 6a, a micromirror array device package usingthe package substrate as shown in FIG. 3 according to further embodimentof the invention is illustrated therein. As seen, package substrate 300is a flat plate with integral heater 220 embedded underneath the surfaceof the package substrate. Micromirror array device 105 is attached toand supported by the package substrate. Spacer 310 is placed on thepackage substrate and forms a space along with package substrate 300 foraccommodating the micromirror array device. Cover substrate 320 isplaced above the spacer and the package substrate. In order to bondingthe package substrate, the spacer and the cover substrate into amicromirror array device package, sealing medium layers 315 and 305 areprovided between the cover substrate and the spacer, and between thespacer and the package substrate, respectively. In the embodiment of theinvention, package substrate 300 and spacer 310 are ceramic.Alternatively, spacer 310 can be, Kovar, Invar, and NiFe_(x). And coversubstrate 320 is light transparent glass. Sealing medium layers 315 and305 are glass frit. During the packaging process, heater 220 iselectrically powered for generating heat so as to melt sealing mediumlayers 305 and 315. Alternatively, external pressure (not shown) can beapplied to enforcing the bonding.

[0047] As an alternative feature of the embodiment, another heater canbe formed in cover substrate 320. The same as the heater in packagesubstrate 300, another heater can be formed along but underneath thesurface of the cover substrate. This heater can be electrically poweredfor generating heat during the packaging process so as to solder sealingmedium layer 315. When the sealing medium layer 315 is metallicmaterial, the heater of cover substrate 320 can be formed on the surfaceof the cover substrate for producing heat so as to soldering sealingmedium 315.

[0048] In another embodiment of the invention, the cover substrate, thespacer and the package substrate can be bonded using solderable metallicsealing mediums. In this situation, sealing medium layers 315 and 305each can be a combination of two metallization layers (e.g.metallization layers 250 and 240 in FIG. 5a) and a sealing medium layer(e.g. sealing medium layer 245 in FIG. 5a) disposed between the twometallization layers. Alternatively, each of the metallization layers ofthe combination can be a multilayered structure that further comprises aplurality of metallization layers. As an example, each sealing mediumlayer 315 or 305 can be a combination of a Au (or Al) layer and a Kovar(or Invar) layer and a Au (or Al) layer, or a combination of a Au (orAl) layer and a Kovar (or Invar) layer and a multilayered structure thatfurther comprises a Au layer and a Nickel layer and a tungsten layer.

[0049] As discussed above, cover substrate 320 is glass for allowingincident light traveling through to shine on the micromirror arraydevice. Alternatively, the cover substrate can be a ceramic or metallicmaterial or any other desired materials that are not transparent tovisible light. In this case, the cover substrate comprises a window withinlay glass for allowing incident light passing through. Alternatively,a glass plate may be mounted on the window of the substrate that is notincident light transparent. As a further alternative feature of theembodiment, a light blocking mask (e.g. a rectangular frame) that blocksincident light around the periphery of the micromirror array device isattached to the surface of the cover substrate, or directly painted orotherwise deposited around the circumference of the cover substrate.This is particularly useful when the cover substrate is glass.

[0050] Other than the flat shape, the cover substrate can be a concavecover cap (not shown) with the lower surface of the cover substrateextended towards the opposite surface (e.g. the top surface) of thecover substrate. In this case, the cover cap and package substrate 300can form a space for housing the micromirror array device without spacer310. Accordingly, the number of metallization medium layers and thenumber of sealing medium layers can be reduced, and bonding process canbe simplified. For example, when cover substrate 320 that is a cover capand package substrate 300 is provided for housing micromirror arraydevice 105, packaging processes described with reference to FIGS. 4a and5 a can be directly applied herein.

[0051] Referring to FIG. 6b, a cross-sectional view of the micromirrorarray package in FIG. 6a is illustrated therein. In addition to thepackaging substrate, the cover substrate, the sealing medium layer andthe metallization medium layers, getters may also be formed within thepackage. The cover light transmissive substrate need not be parallel tothe lower substrate, and the micromirror array device, such as set forthin U.S. patent application Ser. No. 10/343,307, filed on Jan. 29, 2003to Huibers, the subject matter of which being incorporated herein byreference.

[0052] The micromirror array package of the present invention has avariety of applications (e.g. maskless lithography, atomic spectroscopy,maskless fabrication of micromirror arrays, signal processing,microscopy, image sensors/detectors and CCDs etc), one of which is indisplay systems. FIG. 7 illustrates an exemplary micromirror arraypackage according to an embodiment of the invention. The micromirrorarray device is bonded with in the package for protection. Incidentlight can travel through the cover substrate and shin on themicromirrors of the micromirror array device. This package can then beemployed in practical applications, one of which is display systems.

[0053] Referring to FIG. 8a, a typical display system employing amicromirror array device package of FIG. 7 is illustrated therein. Inits very basic configuration, the display system comprises light source102, optical devices (e.g. light pipe 104, lens 106 and 108), colorwheel 103, display target 112 and spatial light modulator 110 that usesmicromirror array device package of FIG. 7. Light source 102 (e.g. anarc lamp) directs incident light through the color wheel and opticaldevices (e.g. light pipe 104 and object lens 106) and shines on spatiallight modulator 110. Spatial light modulator 110 selectively reflectsthe incident light toward optical device 108 and results in an image ondisplay target 112. The display system can be operated in many ways,such as those set forth in U.S. Pat. No. 6,388,661, and U.S. patentapplication Ser. No. 10/340,162, filed on Jan. 10, 2003, both toRichards, the subject matter of each being incorporated herein byreference.

[0054] Referring to FIG. 8b, a block diagram illustrating a displaysystem employing three spatial light modulators, each having amicromirror array device package of FIG. 7, is shown, wherein eachspatial light modulator is designated for respectively modulating thethree primary color (i.e. red, green and blue) light beams. As shown,light 174 from light source 102 passes through optical filters 176 andis split into three primary color light beams, that is, red light 176,green light 178 and blue light 180. Each color light beam impinges aseparate spatial light modulator and is modulated thereby. Specifically,red light 176, green light 178 and blue light 180 respectively impingespatial light modulators 182, 184 and 186 and are modulated. Themodulated red light 188, green light 190 and blue light 192 arerecombined at light combiner 194 for forming modulated color images.Combined color light 196 is directed (e.g. by projection lens) ontodisplay target 112 for viewing. A simplified display system based on theblock diagram of FIG. 8b is presented in FIG. 8c.

[0055] Referring to FIG. 8c, the display system employs a dichroic prismassembly 204 for splitting incident light into three primary color lightbeams. Dichroic prism assembly comprises prisms 176 a, 176 b, 176 c, 176d, 176 e and 176 f. Totally-internally-reflection (TIR) surfaces, i.e.TIR surfaces 205 a, 105 b and 205 c, are defined at the prism surfacesthat face air gaps. The surfaces 198 a and 198 b of prisms 176 c and 176e are coated with dichroic films, yielding dichroic surfaces. Inparticular, dichroic surface 198 a reflects green light and transmitsother light. Dichroic surface 198 b reflects red light and transmitsother light. The three spatial light modulators, 182, 184 and 186 arearranged around the prism assembly. Each spatial light modulatorcomprises a micromirror array device package of FIG. 7 for modulatingincident light.

[0056] Regardless of whether the optical system utilizes a singlemicromirror array package as in FIG. 8a, or multiple micromirror arraypackages as in FIGS. 8b and 8 c, reflection from light transmissivesubstrates is preferably minimized. In operation, incident white light174 from light source 102 enters into prism 176 b and is directedtowards TIR surface 205 a at an angle larger than the critical TIR angleof TIR surface 205 a. TIR surface 205 a totally internally reflects theincident white light towards spatial light modulator 186, which isdesignated for modulating the blue light component of the incident whitelight. At the dichroic surface 198 a, the green light component of thetotally internally reflected light from TIR surface 205 a is separatedtherefrom and reflected towards spatial light modulator 182, which isdesignated for modulating green light. As seen, the separated greenlight may experience TIR by TIR surface 205 b in order to illuminatespatial light modulator 182 at a desired angle. This can be accomplishedby arranging the incident angle of the separated green light onto TIRsurface 205 b larger than the critical TIR angle of TIR surface 205 b.The rest of the light components, other than the green light, of thereflected light from the TIR surface 205 a pass through dichroic surface198 a and are reflected at dichroic surface 198 b. Because dichroicsurface 198 b is designated for reflecting red light component, the redlight component of the incident light onto dichroic surface 198 b isthus separated and reflected onto spatial light modulator 184, which isdesignated for modulating red light. Finally, the blue component of thewhite incident light (white light 174) reaches spatial light modulator186 and is modulated thereby. By collaborating operations of the threespatial light modulators, red, green and blue lights can be properlymodulated. The modulated red, green and blue lights are recollected anddelivered onto display target 112 through optic elements, such asprojection lens 202, if necessary.

[0057] Referring to FIG. 9a, an exemplary micromirror device of themicromirror array device is illustrated therein. As seen, micromirrorplate 136 is attached to hinge 155. The hinge is held by posts 152 thatare formed on substrate 120. With is configuration, the micromirrorplate can rotate above the substrate along the hinge. As alternativefeature, two stoppers are formed for controlling the rotation of themicromirror plate. The substrate is preferably glass. Alternatively, thesubstrate can be a semiconductor wafer, on which standard DRAM circuitryand electrodes can be constructed. FIG. 9b illustrates a micromirrorarray comprising a plurality of micromirror devices in FIG. 9a. Thearray is formed on the upper substrate which is preferably lighttransparent glass. The lower substrate, which is preferably asemiconductor wafer, is formed thereon an array of electrodes andcircuitry for electrostatically controlling the rotation of themicromirrors in the upper substrate. Other than forming the micromirrorarray and the electrode and circuitry array on different substrates asdiscussed above, they can be fabricated on the same substrate.

[0058]FIGS. 9a and 9 b illustrate an exemplary micromirror device havinga micromirror plate with zigzag edges. This is not an absoluterequirement. Instead, the micromirror plate can be of any desired shape.Another exemplary micromirror device with a different configuration isillustrated in FIG. 10a. Referring to FIG. 10a, the micromirror platehas a “diamond” shape. The hinge is arranged parallel to but off-setfrom a diagonal of the micromirror plate. It is worthwhile to point outthat the hinge structure has an arm that is extended towards one end ofthe micromirror plate. The entire hinge structure and the hinge areformed underneath the micromirror plate. This configuration has manybenefits, such as reducing the refraction of the incident light by thehinge and the hinge structure. FIG. 10b illustrates an exemplarymicromirror array device composed of a plurality of micromirror devicesof FIG. 10a.

[0059] As discussed above, sealing medium layers, such as layer 230 inFIG. 4a and layer 245 in FIG. 5a, are preferably layers that comprisematerials with low melting or soldering temperatures. In fact, othersuitable materials with relatively high melting or solderingtemperatures may also be used. In this situation, external coolingmechanisms, such as cooling plates can be employed for dissipating heatfrom the package. For example, a cooling plate can be attached tosubstrate 200 in FIG. 4a and FIG. 4b. Moreover, the present invention isnot only useful in low temperature packaging applications, but also inhigh temperature packaging applications.

[0060] It will be appreciated by those skilled in the art that a new anduseful micromirror array package and methods of applying the same forpackaging micromirror array devices have been described herein. In viewof the many possible embodiments to which the principles of thisinvention may be applied, however, it should be recognized that theembodiments described herein with respect to the drawing figures aremeant to be illustrative only and should not be taken as limiting thescope of invention. For example, those of skill in the art willrecognize that the illustrated embodiments can be modified inarrangement and detail without departing from the spirit of theinvention. In particular, other protective materials, such as inert gas,may be filled in the space formed by the package substrate and the coversubstrate. For another example, the package substrate, as well as thecover substrate and the spacer, can be other suitable materials, such assilicon dioxide, silicon carbide, silicon nitride, and glass ceramic.For yet another example, other suitable auxiliary methods andcomponents, such as applications of Infrared Radiation during bondingfor soldering the sealing medium layers, and pillars or other structuresfor aliening the substrates are also applicable. Moreover, other desiredmaterials, such as anti-stiction material, preferably in vapor phase forreducing stiction of the micromirrors of the micromirror array device,may also be deposited inside the package. The anti-stiction material canbe deposited before bonding the cover substrate and lower substrate.When the cover substrate (e.g. cover substrate 235 in FIGS. 4a, 4 b and4 c) is glass that is visible light transmissive, it can be placedparallel to the micromirror array device (e.g. device 105 in FIGS. 4a, 4b and 4 c) and the package substrate (e.g. package substrate 300).Alternatively, the cover substrate may be placed at an angle with themicromirror array device or the package substrate. Therefore, theinvention as described herein contemplates all such embodiments as maycome within the scope of the following claims and equivalents thereof.

We claim:
 1. A substrate of a package for packaging a micromirror arraydevice, the substrate comprising: a laminate that comprises a pluralityof substrate layers bonded together; and a heater that is disposed alonga periphery of one substrate layer of the plurality of substrate layersand disposed between said substrate layer and another substrate layer ofthe plurality of substrate layers.
 2. The substrate of claim 1, whereinthe heater has a zigzag shape.
 3. The substrate of claim 1, wherein thesubstrate layers are ceramic.
 4. The substrate of claim 1, wherein thesubstrate layers are glass.
 5. The substrate of claim 1, wherein theheater comprises tungsten.
 6. The substrate of claim 1, wherein theplurality of the substrate layers form a cavity in which the micromirrorarray device is located.
 7. The substrate of claim 6, wherein onesubstrate layer of the plurality of substrate layers is depositedthereon a metallization layer for metalizing at least said substratelayer or a glass frit.
 8. The substrate of claim 7, wherein thesubstrate layer, on which the metallization layer is deposited is thesurface layer of the substrate.
 9. The substrate of claim 6, wherein thelaminate comprises an inlay glass that is transmissive to visible light.10. The substrate of claim 1, wherein the laminate is a flat plate. 11.A package, comprising: a first substrate having a heater along aperiphery of the top surface of the first substrate and underneath saidtop surface; a second substrate above the first substrate; asemiconductor device or a microelectromechanical system device betweenthe first and second substrate; and a first sealing medium layer bondingthe first substrate and the second substrate together.
 12. The packageof claim 11, wherein the first sealing medium layer further comprises aglass frit or solderable metallic material that bonds the first andsecond substrates together.
 13. The package of claim 11, wherein thefirst substrate is a multilayered structure that comprises a pluralityof substrate layers.
 14. The package of claim 11, wherein the heater hasa zigzag shape
 15. The package of claim 11, wherein the heater comprisesa metallic material.
 16. The package of claim 15, wherein the metallicmaterial of the heater is formed by sputtering.
 17. The package of claim11, wherein the microelectromechanical device is a micromirror arraydevice that comprises an array of micromirrors for selectivelyreflecting light.
 18. The package of claim 11, wherein the firstsubstrate is ceramic.
 19. The package of claim 11, wherein the secondsubstrate is glass that is transparent to visible light.
 20. The packageof claim 19, wherein at least one surface of the second glass substrateis deposited thereon an anti-reflection layer for enhancing transmissionof visible light through the glass substrate.
 21. The package of claim11, wherein the second substrate further comprises: another heater alonga periphery of a surface of the second substrate and underneath saidsurface of the second substrate.
 22. The package of claim 11, whereinthe first sealing medium layer is a multilayered structure that furthercomprises a plurality of solderable metallization layers for metalizingthe surface of the first substrate.
 23. The package of claim 11, whereinthe first sealing medium layer is a solderable metallization layer formetalizing the surface of the first substrate.
 24. The package of claim23, further comprising: a metallic solder layer on the first sealingmedium layer; and a second sealing medium layer that is solderablemetallization layer between the metallic solder layer and the secondsubstrate for metalizing a surface of the second substrate, said surfacefacing the micromirror array device within the cavity of the firstsubstrate.
 25. The package of claim 11, further comprises: one or moregetters.
 26. The package of claim 11, wherein the first substrate has aconcave surface forming a cavity, in which the semiconductor or themicroelectromechanical device is located.
 27. The package of claim 11,wherein the first substrate is a flat plate, on which the semiconductoror the microelectromechanical device is located.
 28. The package ofclaim 27, wherein the package further comprises: a spacer between thefirst and second substrate; and wherein the first sealing medium layeris between the spacer and the first substrate for bonding the firstsubstrate and the spacer.
 29. The package of claim 28, wherein the firstsealing medium is a glass frit or a solderable metallic layer.
 30. Thepackage of claim 29, wherein the solderable metallic layer that furthercomprises a first metallization layer for metalizing the surface of thefirst substrate, a sealing medium layer for bonding the first substrateand the space together and a second metallization layer for metalizingthe surface of the spacer.
 31. The package of claim 28, wherein thepackage further comprises a second sealing medium layer between thespacer and the second substrate.
 32. The package of claim 31, whereinthe second sealing medium is a glass frit or a solderable metallizationlayer.
 33. The package of claim 32, wherein the solderable metalliclayer that further comprises a first metallization layer for metalizingthe surface of the first substrate, a sealing medium layer for bondingthe first substrate and the space together and a second metallizationlayer for metalizing the surface of the spacer.
 34. The package of claim11, wherein the micromirror array device is a part of a spatial lightmodulator used in a digital display system.
 35. The package of claim 11,wherein the micromirror array device further comprises: an array ofmicromirrors; and an array of electrodes and circuitry forelectrostatically controlling the micromirrors.
 36. The package of claim27, wherein the micromirror array and the electrodes and circuitry arrayare formed on one device substrate.
 37. The package of claim 27, whereinthe micromirror array is formed on a glass substrate that is transparentto visible light; and wherein the electrodes and circuitry array isformed on a wafer.
 38. The package of claim 11, further comprising: oneor more getters.
 39. The package of claim 11, wherein the firstsubstrate has a concave surface that forms a cavity in which thesemiconductor device or the microelectromechanical device being located40. A method comprising: providing a first package substrate thatcomprises a heater integral with and along a periphery of one surface ofthe first substrate; attaching a semiconductor device or amicroelectromechanical device to the first substrate; placing a secondsubstrate on the first substrate with a first sealing medium layertherebetween; driving an electric current through the heater so as togenerate heat for melting the first sealing medium; and bonding thefirst and second substrate by the melted sealing medium.
 41. The methodof claim 40, wherein the heater is embedded underneath the surface ofthe first substrate.
 42. The method of claim 40, wherein themicroelectromechanical device is a micromirror array device thatcomprises an array of micromirrors for selectively reflecting light. 43.The method of claim 40, wherein the heater is formed on the surface ofthe first substrate.
 44. The method of claim 40, wherein the firstsubstrate is a multilayered structure that further comprises a pluralityof substrate layers.
 45. The method of claim 40, wherein the heater ismade up of tungsten.
 46. The method of claim 40, wherein the heater hasan zigzag edge.
 47. The method of claim 40, wherein the first sealingmedium is a glass frit.
 48. The method of claim 40, wherein the firstsealing medium is a solderable metallic layer.
 49. The method of claim40, wherein the first sealing medium is an inorganic material.
 50. Themethod of claim 49, wherein the inorganic material is a metal oxide ormetalloid oxide.
 51. The method of claim 49, wherein the inorganicmaterial is a metal.
 52. The method of claim 40, further comprising:placing the semiconductor device or the microelectromechanical deviceinto a cavity defined by the first substrate; and depositing ananti-stiction material within the cavity.
 53. The method of claim 52,wherein the second sealing medium layer is a solderable metallizationlayer.
 54. The method of claim 52, further comprising: forming anotherheater on in the second substrate such that the heater is along aperiphery of one surface of the second substrate; driving anotherelectric current through the heater on the second substrate.
 55. Themethod of claim 54, wherein the heater in the second substrate isembedded underneath the surface, along the periphery of which the heateris formed.
 56. The method of claim 55, wherein the heater is made up oftungsten.
 57. The method of claim 55, wherein the heater has a zigzagshape.
 58. The method of claim 55, wherein the second substrate is amultilayered structure that further comprises a plurality of layers. 59.The method of claim 54, wherein the first sealing medium layer furthercomprises: a plurality of solderable metallization layers.
 60. Themethod of claim 40, further comprising: during driving the electriccurrent through the heater in the first substrate, applying a pressureon the first and second substrate so as to bonding the first and secondsubstrate.
 61. The method of claim 40, wherein the first substrate has aconcave surface that forms a cavity, in which the semiconductor deviceor the microelectromechanical device is placed.
 62. The method of claim40, wherein the second substrate comprises an inlay glass window that istransparent to visible light.
 63. The method of claim 40, furthercomprising: depositing a rectangular light blocking frame along thecircumference of the second substrate before bonding the first and thesecond substrate.
 64. The method of claim 40, wherein the firstsubstrate is flat; and wherein the method further comprises: beforebonding the first and second substrate, placing a spacer on thedeposited first sealing medium layer and between the first and secondsubstrate; and depositing a second sealing medium layer between thespacer and the second substrate.
 65. The method of claim 64, wherein thesecond sealing medium layer is a glass frit.
 66. The method of claim 64,wherein the second sealing medium layer is a solderable metallicmaterial.
 67. The method of claim 64, wherein the second substratefurther comprises another heater formed along a periphery of one surfaceof the second substrate and embedded underneath said surface of thesecond substrate.
 68. The method of claim 67, further comprising:driving another electric current through the heater in the secondsubstrate.
 69. The method of claim 64, further comprising: depositing afirst metallization layer on a surface of the spacer between the spacerand the second substrate for metalizing the surface of the spacer;depositing a solder layer between the first metallization layer and thesecond substrate; and depositing a second metallization layer along alower surface of the second substrate, said lower surface of the secondsubstrate facing the solder layer and the first substrate.
 70. Themethod of claim 69, wherein the first or second metallization layer is amultilayered structure.
 71. The method of claim 40, further comprising:providing a light source for emitting light shining on the micromirrorarray device; providing a condensing optic element along a path of thelight emitted from the light source and shining on the micromirror arraydevice for directing the light onto the micromirror array device;selectively reflecting the light, by the micromirrors of the micromirrorarray device, onto a display target and; providing a projection opticelement along a path of the reflected light towards the display target.72. The method of claim 40, wherein the step of driving the electriccurrent through the heater further comprises: driving the electriccurrent through the heater so as to heat the surface of the firstsubstrate around 300° degrees or more.
 73. The method of claim 40,wherein the step of driving the electric current through the heaterfurther comprises: driving the electric current through the heater so asto heat the surface of the first substrate around 200° degrees or more.74. The method of claim 40, wherein the step of driving the electriccurrent through the heater further comprises: driving the electriccurrent through the heater so as to heat the first sealing medium to atemperature from 100° to 300° degrees.
 75. The method of claim 40,wherein the first sealing medium has a melting temperature around 300°degrees or less.
 76. The method of claim 40, wherein the first sealingmedium has a melting temperature around 200° degrees or less.
 77. Themethod of claim 40, wherein the semiconductor and the electromechanicaldevice is at a location having a temperature around 70° degrees or lesswhen driving the electric current through the heater.
 78. A system,comprising: a light source for providing light; a spatial lightmodulator for selectively modulating light from the light source so asto form an image on a display target, wherein the spatial lightmodulator further comprises: a first package substrate having a heateralong a periphery of the top surface of the first package substrate andembedded underneath said top surface for generating heat; a micromirrorarray device held on the first package substrate; a second packagesubstrate on the first package substrate; and a first sealing mediumlayer bonding the first package substrate and the second packagesubstrate together; a condensing optical element for directing theincident light onto the spatial light modulator; a display target; and aprojection optic element for directing the modulated light onto thedisplay target.
 79. The system of claim 78, further comprising: a colorwheel having at least three color regions, each corresponding to one ofthe three primary colors including red, blue and green.
 80. The systemof claim 78, wherein the first package substrate has a concave surfacethat forms a cavity, in which the micromirror array device is located.81. The system of claim 78, wherein the first package substrate furthercomprises a plurality of substrate layers.
 82. The system of claim 78,wherein the first package substrate is ceramic.
 83. The system of claim78, wherein the heater in the first package substrate has a zigzagshape.
 84. The system of claim 78, wherein the first sealing mediumlayer is a glass frit.
 85. The system of claim 78, wherein the heater inthe first package substrate is tungsten.
 86. The system of claim 78,wherein the second substrate is glass that is transparent to visiblelight.
 87. The system of claim 86, wherein the glass substrate is coatedwith an anti-reflection layer for enhancing transmission of incidentlight through the glass substrate.
 88. The system of claim 78, whereinthe second package substrate further comprises another heater along aperiphery of one surface of the second package substrate and embeddedunderneath said surface of the second package substrate.
 89. The systemof claim 78, wherein the micromirror array device further comprises: anarray of micromirrors for selectively reflecting the incident light; andan array of electrodes and circuitry for electrostatically controllingthe micromirrors.
 90. The system of claim 89, wherein the array ofmicromirrors and the array of electrodes and circuitry are formed on onedevice substrate;
 91. The system of claim 90, wherein the array ofmicromirrors and the array of electrodes and circuitry are formed onseparate device substrates.
 92. The system of claim 78, wherein thespatial light modulator further comprises: a soldering layer depositedon the first sealing medium; and a second sealing medium deposited onthe soldering layer.
 93. The system of claim 92, wherein the firstsealing medium layer is a solderable metallization layer for metalizingthe surface of the first package substrate; and wherein the secondsealing medium is a solderable metallization layer for metalizing thesurface of the second package substrate.
 94. The system of claim 93,wherein the first or the second sealing medium layer is a multilayeredstructure.